1. Field of the Invention
This invention concerns the field of modular stackable elements formed from tubes, and in particular to such elements employed in large scale playground climbing equipment and small-scale building toys.
2. Description of the Prior Art
Various modular structures for use as playground equipment, toys and the like are known in the art. U.S. Pat. No. 3,974,611 to the present applicant concerns a modular building system based upon a module having triangular faces with internal angles of fifty-five degrees, thirty-five degrees and ninety degrees, and, forty-five degrees, forty-five degrees and ninety degrees. Such modular bodies are useful to stack upwards and outwards. Unlike building systems based upon regular polyhedrons, which build outwards from limited angles, such a system generates frequent regular reoccurring vertical and horizontal surfaces which are useful for building structures. The system of the aforesaid prior patent was based upon polyhedral modules in which each side was formed of sheet material, and various secondary modules were generated from the basic module for certain building needs.
Regarding structures built of sheet materials, a variety of regular polyhedral devices have been patented by Dattner, including U.S. Pat. No. 3,632,109 and others. In order to provide sufficient means for a climber to pass through the internal chambers defined by the polyhedrons of Dattner's design, tubular connecting passageways are required. In any event, even if stacked on facing surfaces, Dattner's modules would not build conveniently into an open-work structure having the maximum of useful vertical and horizontal repeating surfaces.
Various climbing toys for playgrounds and construction toys are based upon tubular elements connected into geometric structures. U.S. Pat. No. 3,974,600--Pearce concerns a building unit, including truncated regular polyhedral modules. The hope of such devices is to form expandable maximum-diversity building systems using tubular subcomponents. Almost invariably, however, such devices are based upon the connection of a plurality of tubular members at a single point or vertex. That is, various tubes radiate from single connection members. In this respect, the basic module of such devices is the single tubular leg, and not a module formed therefrom. Each tubular leg may be considered a part of any of the contiguous surrounding polyhedrons. As a result of such construction, climbing toys and building sets are based upon the strength of individual tubular connections, the connections being at either end of each tube, and not upon the structural integrity of a plurality of modules, each of which is structurally sound of its own construction.
In two dimensions, U.S. Pat. No. 4,219,958--Shulyak is based upon structurally-complete triangles, pivotally attached along co-extensive legs of the triangles. The device employs the structural integrity of individual triangles to form three-dimensional structures which may be varied by altering the hingeable connections. Two-dimensional triangular modules form three-dimensional structures due to frictional pivoting attachments. While such a device is suitable for a toy, it will be appreciated that there is insufficient structural integrity in the structures so formed. The device is therefore not suitable for a playground climbing toy or an expandable building block system.
The present invention only superficially resembles expandable tubular building structures as known in the art. Unlike devices in the art, the invention concerns attaching structurally-complete triangles to form structurally-complete modules, and attaching the modules into various structures. By virtue of the selected angles and truncations, the tubular structure is expandable with great versatility, but is based upon frequently-recurring useful surfaces and building angles.
An intermediate indentation formed in each leg of each triangle can be used as a convenient attachment point for one or more safety and decorative platform members used to close selected triangles of the device. These indentations also provide numerous hand-holds and foot rests which permit a climber to move easily through a structure having openings somewhat larger than that completely spanned by a single step. Accordingly, the invention is both structurally more sound and more easily and safely climbed than structures known in the art.
Interconnection of the rods or tubes forming legs of the triangles may be accomplished in several primarily end-to-end arrangements. The remaining connections involve face-to-face coextensive connections such as the attachment of parallel tubes to join triangles into a module and/or to join modules into a structure. The system is therefore modular in a manner that builds useful openwork structures for playground climbing apparatus and for building toys.